1. Field of the Invention
The present invention relates to a camera module and a method of manufacturing the same.
2. Description of the Related Art
Recently, camera modules are mounted on IT devices such as mobile terminals, PDAs (Personal Digital Assistant), MP3 players and so on. With the development of technology, the resolution of the camera modules changes from 300,000 pixels (VGA) to several million pixels, and the reduction in size and thickness of the camera modules are being performed depending on mounting targets. Further, the camera module provides various additional functions, such as auto-focusing (AF) and optical zoom.
In such camera modules, image sensor modules are mounted, which are manufactured by a COF (Chip On Film) method, a COB (Chip On Board) method, and a CSP (Chip Scale Package) method. The image sensor module is connected to a main substrate through an electrical connection unit such as a PCB (Printed Circuit Board) or FPCB (Flexible Printed Circuit Board).
Recently, however, there is demand for a camera module which can be directly mounted on a main substrate together with general passive elements, thereby simplifying a manufacturing process and reducing a manufacturing cost.
The camera modules are manufactured in such a manner that CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor) image sensors are attached on a substrate by a wire bonding method or flip-chip method. Incident light transmitted through the lens is condensed by the image sensor and is stored as data in a memory. The stored data is displayed as an image through a display medium, such as liquid crystal display (LCD) or PC monitor.
The COF method and the COB method will be described with reference to drawings.
FIG. 1 is an exploded perspective view of a conventional COF type camera module, and FIG. 2 is a partial sectional view of the conventional COF type camera module of FIG. 1.
Referring to FIGS. 1 and 2, the conventional camera module 1 includes an image sensor 3 for converting an image signal inputted through a lens into an electric signal, a housing 2 for supporting the image sensor 3, a lens group 4 for collecting an image signal of an object into the image sensor 3, and a barrel 5 in which the lens group 4 is stacked in multi-layers.
An FPCB (Flexible Printed Circuit Board) 6 is electrically connected to a lower portion of the housing 2. Chip components (e.g., condensers and resistors) for driving the CCD or CMOS image sensor 3 are mounted on the FPCB 6.
In the camera module 1 constructed in such a manner, an ACF (Anisotropic Conductive Film) 8 is inserted between the FPCB 6 and the image sensor 3 in such a state that a plurality of circuit components are mounted on the FPCB 6. Then, heat and pressure are applied to electrically attach the FPCB 6 to the image sensor 3, and an IR filter 7 is attached on the FPCB 6.
Furthermore, in such a state that the barrel 5 and the housing 2 are provisionally screwed to each other, the assembled FPCB 6 is fixed to the bottom surface of the housing 2 by a separate adhesive.
Meanwhile, after the housing 2 to which the FPCB 6 and the barrel 5 are coupled is fixed by an adhesive, an object (resolution chart) is set at a predetermined distance in front of the barrel 5 so as to perform focus adjustment. The focus adjustment of the camera module 1, that is, the focus adjustment between the lens group 4 and the image sensor 3 is performed as a vertical transfer amount of the barrel 5 is adjusted by rotating the barrel 5 screwed to the housing 2.
At this time, the focus adjustment is performed in a state where the distance from the object is set at 50 cm to the infinity. After the focus is finally adjusted, the housing 2 and the barrel 5 are bonded and fixed to each other by an adhesive injected therebetween.
However, when the barrel 5 screwed to the housing 2 is rotated and vertically transferred in order to adjust the focus of an image formed in the image sensor 3 after the barrel 5 having the lens group 4 mounted therein is assembled into the housing 2, foreign matters such as particles, generated by friction at the screw-coupling portion between the barrel 5 and the housing 2, drop down onto the upper surface of the IR filter 7 or the image sensor 3.
Further, the assembling of the FPCB 6 and the housing 2 is determined on the basis of the IR filter 7, which means that the IR filter 7 plays an important roll of adjusting the centers of the image sensor 3 and the lens group 4. Therefore, the mounting position of the IR filter 7 has a large effect upon foreign matters.
That is, as the IR filter 7 is mounted adjacent to the image sensor 3, foreign matters dropping onto the upper surface of the IR filter 7 can be easily recognized. On the contrary, as the IR filter 7 becomes distant from the image sensor 3, an effect caused by foreign matters becomes insensible. Therefore, the camera module needs to be designed in such a manner that the IR filter 7 and the image sensor 3 are spaced at a proper distance from each other.
FIGS. 3 and 4 are diagrams showing a camera module manufactured by the COB method. FIG. 3 is a cross-sectional view of a conventional camera module manufactured by the COB method, and FIG. 4 is an exploded perspective view of the camera module.
In the conventional camera module 10, a printed board 11 having a CCD or CMOS image sensor 12 mounted thereon by wire bonding is coupled to a lower portion of a housing 13 formed of plastics, and a lens barrel 16 having a cylindrical body 15 extending downward is coupled to a barrel 14 extending upward from the housing 13.
In the camera module 10, the housing 13 and the lens barrel 16 are coupled to each other by coupling a female screw portion 14a formed on the inner circumferential surface of the barrel 14 to a male screw 15a formed on the outer circumferential surface of the cylindrical body 15.
At this time, an infrared ray (IR) filter 18 is disposed between a lens L mounted in a lower end portion of the lens barrel 16 and the image sensor 12 attached on the printed board 11, the IR filter 18 cutting off long-wavelength infrared rays incident on the image sensor 12.
In the camera module assembled in such a manner, while light incident from a specific object passes through the lens L, an image is inverted so that the focus is adjusted on the surface of the image sensor 12. At this time, when a focus is optimally adjusted by rotating the lens barrel 16 screwed to the upper end of the housing 13, an adhesive is injected between the housing 13 and the lens barrel 16 such that the housing 13 and the lens barrel 16 are bonded to each other. Then, the camera module is finalized.
Recently, as the resolution and the number of pixels of cameras demanded by users gradually increase, disposal of foreign matters occurring from materials during a manufacturing process is emphasized.
However, there is a limit in securing materials from which foreign matters do not occur at all. Further, as regulations for foreign matter management of materials are tightened, the price of materials inevitably increases, thereby increasing the price of products.
Therefore, to minimize an increase in price of products, materials and parts which are being widely used are utilized. When camera modules are assembled or an inspection process such as image inspection is performed, the following problems occur.
In the conventional camera module, the coupling between the barrel 16 and the housing 13 for performing the focus adjustment is carried out by the rotational structure constructed by the male and female screws 14a and 15a inside the camera module. Therefore, as the coupling portion is abraded by the friction between the male and female screws 14a and 15a, minute particles P occur, thereby considerably degrading an assembling characteristic.
The particles P occurring between the housing 13 and the lens barrel 16 inevitably drop onto the top surface of the IR filter 18 or enter the light receiving region of the image sensor 12. Therefore, when an image is reproduced through the image sensor 12, the particles P may be seen as black spots.